Do you like the idea that youtube ban sexual contents or not? is that a good or bad? I'm with Apple on this issue. Smartphones will take over the world in a year or two, and most teenagers will own one. Not that they can't upload their own. But IMHO, I think it is a right thing to do. You might not like it, but I think it is a good approach for marketing.
Do computer-makers restrict what websites you can visit? No. That would be a stupid idea. How does the fact that the computer is pocket-sized make this any different?
I don't see why a company should decide what's right for me or my family. How is a company going to make the "right" decisions for every household. They can't because every household is different. So give the users the tools to decide for themselves and the tools to lock things out for their kids. Like SG said, put it in an adults-only section and give parents the ability to PW-lock that section.
As for marketing, why restrict yourself to the children/family market when you could market to everyone?